1. Field of the Invention
This invention is related to a method of producing improved silicone rubber compositions. The method yields a product having improved physical properties, particularly tensile strength, when extended with filler.
2. Description of the Prior Art
It is known that siloxane compounds containing hydroxyl groups may be useful additives when added to silicone rubber compositions. U.S. Pat. No. 2,890,188, issued June 9, 1959, to Konkle, McHard, and Polmanteer, teaches that the crepe-hardening of a silicone composition containing an organopolysiloxane and a silica filler having a high surface area could be prevented by adding a hydroxylated organosilane.
U.S. Pat. No. 3,268,473, issued Aug. 23, 1966, to Brown teaches a method of preparing a stable organosiloxane mixture which involves heating a mixture of an organosilicon polymer, a filler, an organosilicon compound containing silicon-bonded hydroxyl radicals and a salt selected from a group consisting of ammonium carbonate and ammonium bicarbonate.
Creamer, in U.S. Pat. No. 3,696,068, issued Oct. 3, 1972, discloses a heat curable silicone gumstock composition comprising 100 parts by weight of diorganopolysiloxane gum containing from about 0.01 to about 1.0 weight percent of vinyl siloxy units and from about 0.5 to about 5 parts by weight of a linear vinyl containing dihydrocarbon siloxane copolymer fluid having endblocking siloxy units of the formula R.sub.3 SiO.sub.0.5. In his Examples, he mixes a polydimethylsiloxane gumstock containing vinyl radical, silica filler, and linear hydroxy terminated dimethylsiloxane oil on a mill. He then hot mills the mixture after it has aged 24 hours at room temperature. After cooling, he mixes the material with a linear vinyl containing dihydrocarbon siloxane copolymer fluid having triorganosiloxy endblocking and a catalyst. The cured rubber has a unique combination of low compression set and high tear strength.
Marinik, in U.S. Pat. No. 4,052,357, issued Oct. 4, 1977, teaches a method of making a silicone rubber composition which provides a combination of high modulus and high tear strength. His method consists essentially of mixing polydiorganosiloxane gum, reinforcing silica filler, hydroxylated diorganosilicon compound having from 10 to 50 percent phenyl radicals and from 2 to 20 percent vinyl radicals, and fiberized blast furnace slag, then heating the mixture. The product can then be catalyzed with vinyl specific organic peroxide and cured into silicone rubber.